The invention is applicable multiple station strip metal forming presses of the type including a vertically reciprocating ram for mounting and operating tools. Such multi-station presses have been manufactured and sold by The U.S. Baird Corporation, Stratford, Conn., under the trademark Multiple Transfer for many years. These presses are well suited for the manufacture of metal parts made sequentially in a succession of drawing operations at the stations. In this type of machine, coil strip stock is fed in widths ranging from a fraction of an inch through up to seven or more inches on the larger machines. Blanks are automatically cut from the strip stock and a vertical blank transfer mechanism positively holds and carries the blank down to the transfer level, where it is picked up by the transfer fingers of a horizontal transfer mechanism. Usually the blank is transferred through a succession of draw dies in as many as fifteen (15) individual work stations and, finally, is ejected as a completed part. This type of completely automatic operation allows piercing, forming, drawing, lettering, embossing and flanging, as well as side slotting, side piercing and reverse drawing at production rates which have exceeded 250 parts per minute. From blanking operation to finished part ejection, all tooling is mounted in standardized precision die sets to facilitate set up and minimize down time. Each station may be individually adjusted or serviced. Complete die sets can be interchanged without losing tool adjustment. Frequent complete change of jobs or intricate toolings will justify extra die sets.
An example of an early press of this type developed by the assignee of the instant invention which sets forth the essential nature of this type of press is found in U.S. Pat. 2,049,915 dated Aug. 4, 1936, in the name of Arthur J. Lewis and assigned to the assignee of the instant application. Of course, a large number of improvements have been made since the issuance of the Lewis patent, primarily with a view toward producing higher speeds, lower ultimate tooling costs, precision operation, tool adjustment and replacement, minimizing down time, minimizing scrap loss and, in general, providing greater versatility and operational sophistication for the presses. Some of the advancements in multi-station strip metal forming presses are set forth in my U.S. Pat. 4,166,372 issued Sept. 4, 1979 for a Multi-Station Transfer Press Having A Punch-Extending Means, my U.S. Pat. No. 4,406,148 issued Sept. 27, 1983 for a Multi-Station Transfer Press Having Transfer Slide Safety Release Means, and my U.S. Pat. No. 4,655,071 issued Apr. 7, 1987 for a Transfer Press with Quick-Change Die Set Arrangement.
As the speed and sophistication of the multi-station metal forming press have increased, the transfer fingers of the horizontal transfer mechanism have become a limiting factor in speed of operation and quality of the final part. The horizontal transfer mechanism, which carries parts to the next sequential station between forming strokes of the press, generally comprises two transfer rails having opposed pairs of inwardly extending fingers. The fingers are spring biased inwardly and are cammed outwardly to accept and grip parts and to clear the punches and dies. For this purpose, the fingers have an end pad which includes leading and trailing cam surfaces flanking a concave recess for partially surrounding and holding the part. Two opposed fingers thereby together engage, hold and support the part during transfer from one station to the next sequential station. The fingers are often provided with upper and lower inclined cam surfaces as well, so that vertically moving parts and/or portions of the tool and die set will cam the fingers to the open positions for clearance, as required, to engage and release parts.
The camming of the fingers has several drawbacks. First, the finger pads themselves are subject to wear and accordingly must be fabricated of steel to achieve long life. Even though the steel may be highly polished or even chrome plated, the camming of the fingers over the parts tends to leave scratches and marks on the parts. If a smooth, scratch-free surface is desired on the part for esthetic or functional reasons, these scratches caused by the transfer fingers must be polished out. Also because of the manner in which the finger pads cam over the parts, the portion of the finger pad engaging the part is limited to provide a relatively easy engagement and release of the part. All of these factors have an effect on the speed of operation of the metal forming press as well as the quality of the parts produced thereby.